Flexible Spectrum Use and Laws of Physics Prof. Ryszard Struzak r.struzak@ieee.org ITU Seminar...

Flexible Spectrum Use and Laws of Physics

Prof. Ryszard Struzak

r.struzak@ieee.org

ITU Seminar "Economic aspects of national radio frequency spectrum management”

Kyiv, Ukraine, 03-05 July 2007

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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Flexible use concept

• Matheson RJ: Flexible Spectrum Use Rights•Tutorial at International Symposium on Advanced Radio Technologies (ISART) 2005

• Spectrum traded, aggregated, divided and freely used for a wide range of user-selected services, under 2 rules only:

– Transmit within signal power restrictions inside your licensed ‘electrospace’ region

– Keep your signals below ‘X’ outside your licensed region

Note: Not applicable to passive services!

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Household analogy

• In your house, you are free to arrange your furniture at will

• Flexible Spectrum Use Rights are expected to offer similar freedom in using the RF spectrum.

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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Radio wave propagation

• „Flexible use” rules – Inside the licensed region the signal must be strong

as required by the service offered there – Outside the licensed region the signal must be weak -

otherwise it disturbs services offered there

• imply the signal to change at the border

• Problem: radio wave in a continuous medium decays gradually – it cannot change abruptly

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• The signal power can fall naturally to level ‘X’ only at a distance dx from the transmitter

• ‘dx’ determines sterile region where other systems cannot use the same frequency resources (compare „frequency reuse distance”)

• The flexible spectrum use doctrine disregards that fact.

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1

X

1 dx

‘Outside’ limit

Natural signal power decay

Distance (normalized)

Sig

nal p

ower

(no

rmal

ized

)

Service region used

Propagation (simplified model)

Sterile (denied) region

Signal power limit (rule #2)

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Covered-to-sterile area ratio

0.01

0.1

1

0.01 0.1 1

X: Out-of-coverage to in-coverage signal power ratio

Y: C

over

ed-to

-den

ied

area

rat

io (c

ircl

e)

Propagation exponent = 2

3

4

Used

Sterile (Denied)

Rural

Urban

Omnidirectional antennas

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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A new look at radio transmission

• A radio signal has a number of measurable characteristics (dimensions) that create a multidimesional space (hyperspace)

• Signal hyperspace - a set of orthogonal variables by which one radio signal can be distinguished from another. Frequency, modulation, power, direction and coding are examples.

• Signals → solids in the hyperspace • Radio transmission → a series of signal

mappings

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• Transmitter: – maps the original message (mi) into the

radiated radio wave

• Propagation process: – maps it into the incident wave (sij) and

introduces noise, reflections, latency, fading, Doppler Effect, etc. - many of these effects are uncontrollable!

• Receiver: – maps incident wave into the recovered

message (mij) that (normally) is close to the original message

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Radio transmission = mapping

Radiatedwave

(wanted)

Incidentwave

4. Recoveredmessage

1. Original

message

B. Propagation

mappingA.

Transmittermapping

C. Receivermapping

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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• The radiated wave reaches the intended receiver(s) and other receivers

• The incident wave at each receiver is a combination of the intended signal, noise and a number of unintended signals

• The service (quality, range, coverage, etc.) depend on the power ratio of the intended-to-unintended signals (congested environment)

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• There is

a multitude of radio

transmitters (Tj)

and receivers (Rj)

in operation

→ congestion!

mji

Ti Rj+

+

+

mi

sij

Nj

Blue = Wanted

Red = Unintended

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Successful transmission #1

• The intended signal must fit the receiver input „window” in all dimensions

x1

x2

1) x1=Time, x2 = Frequency2) x1=Power. x2 = Frequency3) x1=Frequency. x2 = Timeetc.

Signal projection on (x1, x2)

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• Receiver responds only to the incident-wave components that fall into its „reaction window”– The intended signals must appear at correct

time and frequency, from correct direction, with correct polarization and coding, etc.

• Receiver reaction window: – a single opening (analog systems) or – a set of non-contiguous openings (digital

systems)

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Successful transmission #2

• All unintended signals must be rejected – they must be

outside the receiver reaction window

window

signal

x1

x2

x1

x2

Signal projections

1) x1=Time, x2 = Frequency2) x1=Power. x2 = Frequency3) x1=Frequency. x2 = Timeetc.

Signal projection on (x1, x2)

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• To be rejected, an unintended signal must be sufficiently distant from the receiver’s reaction window in at least one variable– It must appear at wrong times, at wrong frequencies,

wrongly coded etc.

• The “sufficient” distance is system dependent and might be defined in

• geographical domain (e.g. frequ. re-use distances), • frequency domain (e.g. frequency plans), • power domain (as in ultra-wideband systems sharing

frequencies with narrow-band systems), • time domain (e.g. TDMA systems)• coding/ spreading domain (as in spread-spectrum systems)• direction domain (antenna directivity)• etc., plus any combination

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3D illustration

Distance East

Fre

quen

cy

Distance

North Service regions

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Unintended interactions: effects

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2

x / Max. Range

y / M

ax. R

ang

e

n = 1Coverage loss = ~35%

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2

x / Max. Range

y / M

ax. R

ang

en = 1Coverage loss = ~50%

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1.2 -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2

x / Max. Range

y / M

ax. R

ang

e

n = 6Coverage loss = ~75%

35% 50% 75%Loss:

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• Household analogy:– House walls made of

a rubber membrane – under the neighbors’

pressure, the house changes its size and form

– no more flexibility in the furniture arrangement!

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• Unintended interactions are critical factors

• Problems: – They depend not only on specific characteristics

of individual systems, but also on their number and spatial deployment that are out of control (as a principle)

– Their possible control reduces greatly the freedom in RF spectrum use

– The doctrine of flexible use disregards that fact

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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Open questions

• Due to unintended interactions, each new transmitter operating nearby reduces the service (range and/or quality) and so do profits– How does it influence the investment decisions?– How does it depreciate the business value? – Could it be compensated?

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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Trends #1

• The more signal dimensions used by the system, the more degrees of freedom and more flexibility in the use of the RF spectrum resources

• There is no limit imposed a priori on signal dimensionality employed and additional dimensions (variables) are included as spectrum congestion increases, rational spectrum management evolves, and radio technology develops

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Trends #2• Static approach to spectrum use

dynamic approach

• Spectrum management rules and practices built-in in the equipment hardware/ software and executed automatically (communication protocols, rules, strategies, policies)

• Competition in the spectrum use collaborative approach

• Competition among the spectrum users competition among equipment manufacturers

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Self-organizing & learning systems operating like ants thatassist each other in fulfilling their tasks - New business model

http://ant.edb.miyakyo-u.ac.jp/INTRODUCTION/Gakken79E/Page_04.html

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Outline

1. Flexible Spectrum Use

2. Radio wave propagation

3. Signal hyperspace

4. Unintended interactions

5. Open questions

6. Trends

7. Concluding remarks

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Concluding remarks

• Flexible spectrum use doctrine is an interesting concept deserving further exploration

• It is applicable to a wide range of active services but is not applicable to passive services.

• It disregards some physical constraints due to unintended interactions and radio propagation

• It requires „intelligent communication robots” -- self-organizing systems able to learn and adapt automatically/ dynamically to the environment

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• With „Classic” radio technology, flexible-use spectrum rights can be exercised only when the system in hand is isolated, or when it does not require any protection against interference and it does not disturb other systems.

• New technologies of „intelligent communication robots” make practical the concept of flexible spectrum use rights

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• Physical constraints do not depend on spectrum management regime (static or dynamic) and spectrum use rights

» They are the same when the spectrum resources are treated a private property or as an open commons, administratively regulated, or self-regulated through market forces

• Unintended interactions with other systems determine system performances to the same degree as intended ones

» Interacting systems behave as a network» Operation of systems in the network must be

harmonized/ coordinated

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Thank you for your attention